Isolation of radio frequency losses in oscillator and wave guide systems



Sept. 24, 1957 2,807,745

J. L. MOLL ISOLATION OF RADIO FREQUENCY LOSSES IN OSCILLATOR AND WAVE GUIDE SYSTEMS Filed July 12, 1951 2 Sheets-Sheet 1 II==- l w CAPACITATIVE-l BY-PASS -3 5 /3 9 o OUPLING SECTION 'I l. I! WAVEGUIDE" REPELLER IN VENTOR se t. 24, 1957 J. .MOLL 2,80

I ISOLATION OF R O FREQUENCYLOSSES IN OSCILLATOR AND WAVE GUIDE SYSTEMS Filed July 12, 1951 2 Sh t ee s-Sheet 2 INVENTOR w made John L. Moll, Columbus, Ohio, assignor to The ()hio State University Research Foundation, Columbus, Ohio,

a corporation of Ohio Application July 12, 1951, Serial No.'236,37t A 1 6 Claims. (Cl. 315-512) My invention relates broadly ot high frequency oscillator and waveguide systems and more particularly to a composite oscillator and waveguide having means for isolating and minimizing electrical losses.

One of the objects of my invention is to provide a composite oscillator and waveguide system for operation at high frequencies including means for isolating radio frequency losses and minimizing such losses for securing a high degree of'electrical efficiency in the oscillator and waveguide.

Another object of my invention is to provide a construction of oscillator and waveguide of such characteristics that devices in accordance with the invention may be reproduced on a mass production scale with such tolerances as will assure a high degree of efficiency in operation of the devices.

Still another object of my invention is to provide a construction of oscillator and waveguide system including an adjustable repeller controllable in position in the resonant cavity of the oscillator and waveguide for tuning the system over a relatively wide range while maintaining electrical losses at a minimum for all operating frequencies.

,l A still further object of my invention is to provide a composite oscillator and waveguide system including an electron emitter and an associated adjustable repeller operative to tune the system by capacitative tuning with associated decoupling means designed to assure operation of the system at high electrical efficiency over a substantial operating range.

Other and further objects of my invention are to provide an arrangement of waveguide output for reflex oscillators having means for isolating the repeller from radiofrequency losses as set forth more fully in the specification hereinafter following by reference to the accompanying drawings in which:

Figure 1 is a vertical longitudinal sectional view taken through the composite oscillator and waveguide system of my invention with certain of the parts illustrated in elevation'and showing particularly the manner of adjusting the repeller through the resonant cavity and with referenceto the decoupling section of the waveguide; Fig; 2 is a horizontal'sectional view drawn on a reduced scale and taken substantially on line 22 of Fig. 1; Fig. 3 is a transverse vertical sectional view taken through the composite oscillator and waveguide substantially on line 3-3 of Fig. l and showing certain of the parts in elevation; Fig. 4 is avfragmentary horizontal sectional view taken'substantially on line 44 of Fig. 3; Fig. 5 is an end viewof the waveguide on a reduced scale lookingin the direction of arrow A in Fig. l; and Fig. 6 diagrammatically illustrates the electrical circuit equivalent of the oscillator and waveguide of my invention.

My invention is directed to a method for constructing non-contacting, radio frequency shorts in high frequency oscillators and waveguides which has the two desirable properties that: I

atent O shorting device the non-contacting short in the useful load.

In general, high-frequency oscillators consist of:

(1) An electron stream which gives up energy to a radio-frequency electrical field.

(2) A resonant circuit, usually a resonant cavity, which stores radio frequency energy and maintains a strong electrical field in a region of interaction between the electron stream and the field.

(3) Acoupling device to extract some of the energy from the resonant circuit and deliver it to an external load.

,The structureshown in the drawings embodies the last mentioned functionsnumbered 2 and 3 by utilizing the novel method of non-contacting shorting device which simultaneously performs the functions of providing a non-contacting short circuit and extracts energy from the resonant circuit.

Referring to the drawings in more detail reference character 1 designates generally the cathode and heater of the oscillator arranged adjacent the beam focusing elements designated generally at 2. The beam focusing elements. 2a is insulatingly spaced from the beam focusingelement 2b by spacing insulator 12 which extends between the metallic section or electrically conductive header 14 of the oscillator and waveguide that is recessed to provide the resonant cavity 4. The beam focusing.

element 2b is in the form of a comically shaped orifice for concentrating a dense beam of electrons which is projected veritically through the resonant cavity 4 and into the central recess 5a formed in the depending end of the adjustable repeller 5. Repeller 5 is shaped in a very particular manner as its terminus 5b is trapered from the solid cylindrical section 5 to an annular peripheral tip 50. As the repeller 5 is adjusted upwardly the tapered surface 5b increases the spacial gap between the surface of the repeller 5 and the decoupling section. The resonant cavity 4'is contained within the header 14 of the waveguide 6 and terminates in a decoupling section 9. The decoupling section is in the shape of a hollow cylindrical metallic wall structure which projects upwardly through aperture'6a ,in the lower wall of the waveguide 6 and intothe interior of the waveguide 6 for a distance less than one half the depth of the waveguide. The upper wall of the waveguide 6 is apertured as represented at 6b and with which there is aligned the aperture 15a in the metallic section or electrically conductive header 15 which extends across the top of. the waveguide. The headers 14 and 15 both extend beyond the peripheral limits of the external dimensions of the waveguide. Thealigned inner surfaces of apertures 6b in the top of the waveguide and the inner surface of aperture 15a of the metallic header 15 form a capacitative area which coacts with a cylindrical capacitative by-pass member .10 which is carried by the adjustable repeller 5. The capacitative by-pass member 10 is spaced from the capacitative area formed by the inner peripheries of surfaces 6b and 15a so that axial adjustment of repeller 5 in an upward direction tends to reduce the overlapping of the adjacent capacitative surfaces of capacitative by- 1 pass 10 and surfaces 6b, 15a, reducing the effective bypass capacity as 'therepeller 5'is withdrawn from the re- Patented Sept. 24, 1957 sonant cavity 4 and correspondingly enlarges the gap spacing at 3 between the terminus of the repeller 5 and the conically shaped end of the beam focusing element 2b. This adjustment is accomplished by means of a flexible metallic bellows 8 supported on metallic header 15 and extending upwardly into connection with the cylindrical section 16 which supports the disc-like insulator 17 mounted on the shaft extension 5d of the repeller 5. Thus repeller 5 is insulatingly centered with respect to the oscillator and waveguide in spacial relation to the decoupling section 9, formed by the annular surface 4a contiguous with the upper portion of the resonant cavity 4 and the inner surface 9a of the decoupling section 9, and the capacitative by-pass section formed by surfaces 6b and 15a, coacting with the cylindrical surface of capacitative by-pass 10.

It will be understood-that the decoupling section of the oscillator and waveguide is constituted by the conjoint cylindrical surfaces 4a and 9a through which the cylindrical repeller 5 is adjusted. The capacitative by pass section is constituted by the conjoint surfaces 6b and 15a coacting with the cylindrical surface 10. The tapered surface 5b of the repeller 5 as it advances into the decoupling sectionforrned by surfaces 4a and 9a increases the size of the capacitative gap 18 between the oscillator and waveguide and the repeller 5.

The waveguide 6 includes an electrically shorted section 6c shown to the left of the oscillator in Figs. 1 and 2 and presenting aniinfinite impedance to the de coupling section 9. The oscillator is located at the input end of the waveguide 6. The output end of the waveguide 6 is shown at the right in Figs. 1 and 2 at 6d and terminates in its characteristic impedance Z The output section 6d of the waveguide terminates in flanges 11 between which the disc 7 is sealed as a gasket. The oscillator and waveguide are vacuum sealed but for the purpose of clarification in illustrating the invention the seals have not been detailed. It will be understood, however, that such seals are provided at all joints for maintaining the oscillator and waveguide under vacuum.

In Fig. 6 I have illustrated the approximate electrical circuit for the oscillator and waveguide system of my invention. The resonant circuit formed by the structure has been designated by inductance LR and the capacitance CR- The lineof length 0 and characteristic impedance Z'r between points A and B represents the decoupling section. C represents the capacitative by-pass and Z0; represents the terminating impedance. Inasmuch as the parts of the oscillator and waveguide are precision made for predetermined operating frequencies, mass production of the equipment having substantial uniform characteristics is assured.

In practice, the reactance of C is small compared to Z0; and its effect may be neglected. The decoupling section is most effective when it is a quarter of a wavelength long. In this case the resistance presented to the resonant circuit is Thus the degree of coupling, or decoupling, of the resonant circuit can be adjusted by adjusting the value of 211.

In operation, the repeller is maintained at a voltage negative with respect to the cathode 1 and the cavity 4 is positive with respect to the cathode 1. The tube is tuned by moving the repeller 5 in an axial direction, changing the gap spacing at 3 that is by capacitive tuning. The length of the decoupling section 9 is made to be a quarter of a wave length at the short wave length end of the operating range, and its characteristic impedance is adjusted to give satisfactory operation over the range. The equivalent electrical circuitis as set forth in Fig. 6.

I have constructed and successfully operated tubes in accordance with this invention which have produced power outputs in excess of of a watt over the range from 2.2 to 4 centimeters. This result would be impossible using conventional methods of obtaining noncontacting shorts and extracting energy from the tube. The spacing required for a satisfactory conventional noncontacting short between the repeller and the cavity block would be approvimately 0.001 (one thousandth) of an inch. The spacing used in the oscillator of my invention is .010 (ten-thousandths) of an inch.

The structure of the composite oscillator and waveguide is such that the diameter of the decoupling section is substantially less than the diameter of the capacitative by pass section. Also the diameter of the decoupling section 9 is less than the diameter of the cavity resonator 4. The linear dimension of the cylindrical surface 10 is such that it normally projects beyond header 15 at one end when the other end thereof is coplanar with the inner wall of the waveguide and when the repeller is adjusted to a position of minimum gap length at 3 for discharge of electrons from the cathode 1 through the beam focusing elements 2. Tuning is accomplished by axial movement of repeller 5 in such manner that the gap 3 is changed, the distance between tapered surface 5b of repeller 5 and the interior surfaces 4a and 9a of decoupling section 9 changes and the capacitative by-pass condition changes as cylindrical surface 10 moves out of overlapping relation with surfaces 6b and 15a foretfecting tuning at one end of the operating range. When tuning toward the other end of the operating length the overlapping relationship of capacity area 10 and surfaces 6b and 15a increases while the gap 18 between the repeller 5 and surfaces 9a and 4a becomes more uniform inasmuch as the tapered portion 5b of repeller 5 moves out of overlapping relationship with surface 4auat the same timeithat gap 3 is being narrowed.

While I have described my invention in certain of its preferred embodiments I realize that modifications may be made and I desire that it be understood that no limitations upon my invention are intended other than may be imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A combined oscillator and waveguide comprising a tubular metallic waveguide having an input section and an output section, electrically conductive headers extending in electrical contact with the opposite outside walls of said waveguide in positions adjacent said input section, said headers being apertured and opening into said waveguide, a resonant cavity included within one of said headers, an oscillator located in said resonant cavity, the opposite walls of said waveguide being aperturcd along an axis normal to the axis of said waveguide for establishing a wave path into said headers with the aperture in one wall exceeding in diameter the aperture in the opposite wall, an axially adjustable repeller extending through said headers and the apertures in the opposite walls of said waveguide and projecting into said resonant cavity, a cylindrical member constituting a cylindrical capacity area mounted on said repeller in the region thereof which passes through one of said headers and the aperture in the adjacent wall of the waveguide and establishing an adjustable capacitative bypass relation therewith, the other of said headers having a cylindrical sleeve connected therewith and extending through the adjacent apertured wall of said waveguide and projecting into the waveguide for establishing a decoupling relation between said oscillator and said waveguide, and means for mounting said repeller for axial adjustment through said capacitative ;by-pass, said cylindrical sleeve and said resonant cavity.

2. A combined oscillator and waveguide as set forth in claim l in which the transverse dimension of said cylindrical sleeve is substantially less than the corresponding dimension of said cylindrical member.

3. A combined oscillator and waveguide as set forth in claim 1 in which the peripheral limits of both of said headers project beyond the peripheral limits of the end wall and the side walls of the waveguide at the input end thereof.

4. A combined oscillator and Waveguide as set forth in claim'l in which said repeller is tapered adjacent the end thereof whereby adjustment of said repeller tending to withdraw the tapered end of said repeller from said cavity through said cylindrical sleeve increases the capacitative gap between said repeller and the interior wall of said sleeve and 'contrawise movement of the tapered end of said repeller toward said cavity decreases the capacitative gap between the interior wall of the cylindrical sleeve and the tapered end of the repeller.

5. A combined oscillator and waveguide as set forth in claim 1 in which said cylindrical member constituting the cylindrical capacity area establishes capacitative relation with both the edge of the aperture in said waveguide and the header associated therewith and wherein said cylindrical member has a linear dimension such that the cylindrical capacity area constituted thereby normally projects beyond the associated header at one end when the other end thereof is coplanar with the inner wall of the waveguide and when the repeller is adjusted to a limiting operating position within said resonant cavity.

6. A combined oscillator and waveguide is set forth in claim 1 in which said cylindrical sleeve is an integral part of said last mentioned header and projects through the adjacent apertured wall of the waveguide for a distance less than one half the depth of the waveguide.

References Cited in the file of this patent UNITED STATES PATENTS 

